Field of the Invention
The invention relates to cutting tools, and in particular to a method of making coolant passages in a rotary cutting tool using electro-magnetic radiation.
Description of Related Art
Electrical discharge machining (or EDM) is a machining method primarily used for hard metals or those that would be impossible to machine with traditional techniques. One critical limitation, however, is that EDM only works with materials that are electrically conductive. EDM can cut small or odd-shaped angles, intricate contours or cavities in extremely hard steel and exotic metals, such as Titanium, Hastelloy, Kovar, Inconel and carbide.
Sometimes referred to as spark machining or spark eroding, EDM is a nontraditional method of removing material by a series of rapidly recurring electric arcing discharges between an electrode (the cutting tool) and the work piece, in the presence of an energetic electric field (applied potential). The EDM cutting tool is guided along the desired path very close to the workpiece, but it does not touch the workpiece. Consecutive sparks produce a series of micro-craters on the work piece and remove material along the cutting path by melting and vaporization. The particles are washed away by the continuously flushing dielectric fluid.
Electro Chemical Machining (or ECM) is a method of working extremely hard materials or materials that are difficult to machine cleanly using conventional methods. It is limited, however, to electrically conductive materials. ECM can cut small or odd-shaped angles, intricate contours or cavities in extremely hard steel and exotic metals, such as Titanium, Hastelloy, Kovar and Inconel.
ECM is similar in concept to EDM in that a high current is passed between an electrode and the part and through an electrolyte. While the applied potential in EDM ranges from 20 to 200V, the applied potential in ECM is lower and ranges from a few mV to about 30V. The ECM cutting tool is guided along the desired path very close to the work but it does not touch the workpiece. Unlike EDM however, no sparks are created. The workpiece is corroded away by the electro-chemical reaction occurring at the surface of the workpiece. Very high metal removal rates are possible with ECM, along with no thermal or mechanical stresses being transferred to the part, and mirror surface finishes are possible. The ECM process is most widely used to produce complicated shapes with good surface finish in difficult to machine materials, such as turbine blades. It is also widely used as a deburring process.
Both the ECM and EDM processes use electrical current under direct-current (DC) voltage to electrically power removal of the material from the workpiece. In ECM, an electrically conductive liquid or electrolyte is circulated between the electrodes and the workpiece for permitting electrochemical dissolution of the workpiece material, as well as cooling and flushing the gap region therebetween. In EDM, a nonconductive liquid or dielectric is circulated between the cathode and workpiece to permit electrical discharges in the gap therebetween for removing the workpiece material.
In both ECM and EDM the corresponding electrodes thereof are typically mounted in multi-axis NC machines for achieving the precise 3D feed path required thereof for machining complex 3D workpieces, such as the airfoils of blades and vanes. The NC machines include digitally programmable computers and include suitable software, which controls all operation, including the feed path and the separate ECM and EDM processes.
Electrical arcing during the ECM or EDM processes can result in a relatively large recast layer or heat affected zone (HAZ) on the machined workpiece, such as a cutting tool, in which the material properties can be undesirably degraded. Specifically, electrical arcing during the ECM or EDM processes can result in a relatively large recast layer or heat affected zone (HAZ) on the machined workpiece in which the material properties can be undesirably degraded. Thus, in both processes, electrical arcing between the ECM or EDM electrodes and the workpiece, such as a cutting tool, must be prevented to prevent undesirable heat damage to the cutting tool.
Accordingly, it is desirable to provide a method of making coolant passages in a cutting tool without undesirable damage to the material properties of the cutting tool.